CVE-2024-11113 - Unpacking the Use-After-Free Bug in Chrome’s Accessibility—What You Need to Know

On March 13, 2024, Google assigned CVE-2024-11113 to a medium-severity bug in their Chrome browser. The bug, a classic use-after-free in the accessibility (a11y) code, was patched in version 131..6778.69. This one slipped into Chrome’s renderer and, if you know your way around, could be abused for heap corruption through a tricky HTML page. Let’s break down what happened, look at the basics of use-after-free, and see why this issue matters (plus, provide some code examples and resources for deeper digging).

What Is a Use-After-Free?

Before diving into the exploit, let's recap: a use-after-free (UAF) occurs when a program continues to use memory after it's been freed. This often leads to heap corruption or execution of attacker-controlled code.

In browsers, UAF is especially dangerous since they handle user-supplied content. If an attacker leverages a UAF, they might escape the sandbox, execute code, or just crash the renderer—bad news any way you slice it.

The Bug: Accessibility Mishandling

For CVE-2024-11113, the problem sat in Chrome’s accessibility module—the component that makes web content readable for screen readers and other assistive technologies.

A compromised renderer process (which could mean malicious code is already running in a lower-privileged context) could send carefully crafted HTML to the accessibility engine, leading the browser to reference memory after it’s been freed.

Here’s a summary in Google’s words

> Use after free in Accessibility in Google Chrome prior to 131..6778.69 allowed a remote attacker who had compromised the renderer process to potentially exploit heap corruption via a crafted HTML page. (Chromium security severity: Medium)

Reference:
- Chromium Security Advisory (CVE-2024-11113)

The direct exploit scenario goes like this

1. Renderer Compromise: The attacker gets code execution in the renderer process, maybe via another JavaScript vulnerability or drive-by malware.
2. Heap Manipulation with Accessibility: The exploit crafts special HTML to trigger a UAF in the accessibility code. By manipulating the DOM and triggering accessibility updates, the code frees an object but later references it, causing heap corruption.
3. Attacker Payload: Given careful heap spraying or memory layout manipulation, the attacker can control what memory gets accessed, sometimes even controlling the program flow.

Exploit Example (Simplified)

Below is a simplified code snippet (not a working exploit, just to illustrate the concept). If you're a developer or security pro, this can help you imagine how attackers approach memory corruption bugs.

Let’s pretend there’s an object in the accessibility layer that processes events on a DOM node. If you can free it (e.g., by removing it from the DOM) but still trigger code that accesses it, you hit use-after-free.

// WARNING: This is for educational purposes, not an actual proof-of-concept exploit.

let node = document.createElement('div');
document.body.appendChild(node);

// Trigger accessibility initialization
node.setAttribute('role', 'button');

// Schedule removal and access
node.addEventListener('focus', () => {
    setTimeout(() => {
        document.body.removeChild(node); // Potentially frees accessibility objects
    }, );
    // Here, we might trigger a scenario where accessibility code
    // still tries to use the object after it's been freed
});

// Simulate accessibility API call (or in real-world, convince browser to focus the node)
node.focus();

In real exploits, attackers craft complex DOM states and interactions to hit the race condition leading to UAF and heap corruption.

Why It’s Not Critical

CVE-2024-11113 is rated Medium just because it requires the attacker to already compromise the renderer process. That means you need another bug, like a JavaScript engine exploit, to get to this vulnerability. In other words, it’s mostly a sandbox escape step—not a standalone remote code execution problem.

What Should You Do?

Update Chrome. That’s the most important takeaway. Ensure your version is at least 131..6778.69 or newer. Google patches security bugs quickly, so regular updates keep you safe.

For developers:

For More Information

- Chromium Release Notes for 131..6778.69
- Chromium Bug Tracker - (May require permissions)
- Google Project Zero: Exploiting Chrome Renderer Bugs

Summary

*CVE-2024-11113* highlights the ongoing battle to keep browsers safe, especially from attacks on the accessibility code that handles user-facing features. While this bug hasn’t (yet) been publicly exploited, it shows how even little-used features can become attack vectors. The best defense, besides technical mitigations, is staying updated—so patch your Chrome and surf safely!


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Timeline

Published on: 11/12/2024 21:15:11 UTC
Last modified on: 01/02/2025 18:02:23 UTC